Medical procedures have been developed in which body implantable electrical signal generators are implanted in the body which generate electrical signals for stimulating parts of the body with the electrical signal generated by the signal generator. The most common type of body implantable electrical signal generator is the heart pacemaker. Procedures are well developed for implanting heart pacemakers. Additionally, other implantable electrical signal generators exist such as defibrillators and nerve stimulators which generate electrical signals for application to the heart and the nerves respectively.
FIGS. 1 and 2 illustrate a prior art heart pacemaker 10 which has been implanted in the body 12 of a person by an incision 14. An electrical lead 16 couples an electrical signal generated by signal generator 18 to the heart 20. The electrical lead 16 is connected to a connector assembly 22 which completes an electrical connection to the signal generator 18 retained within housing 24. The incision 14 is typically made on the anterior superior chest wall 3 to 4 centimeters inferior to the mid-portion of the clavicle and cut to the level of the pectoral fascia. A pocket is formed within the patient's body for retaining the pacemaker 10. The electrical lead 16 is introduced into the subclavian vein 26 or cephalic vein and hence into the subclavian vein and forwarded down into the right ventricle of the heart 20 where the end thereof is attached to the ventricle to receive the electrical signal generated by the signal generator.
FIG. 1 illustrates an undesirable implantation of a pacemaker 10 in that the electrical lead 16 is too long for the distance between the connector 22 and the right clavicle. The portion 27 of the electrical lead 16 is redundant. Redundant lead wire 27 produces a bulge which can occur anywhere in the redundant lead. When the redundant lead wire 27 is wrapped around the periphery of the pacemaker, perpendicular to the thickness of the pacemaker (which is the desired positioning of redundant lead wire in a surgical procedure for implanting a pacemaker), bulging can load the redundant lead wire which applies a force to the lead along its longitudinal axis. As a result of the relative stiffness of the electrical lead 16, this force can potentially be transmitted to the ventricular wall of the heart with the possibility of perforation of the ventricular wall where the tip of the electrical lead 16 is attached to the ventricular wall. Loading in the other direction can cause bulging of the lead in or near the pocket resulting in patient discomfort.
FIG. 2 illustrates the optimal prior art procedure for implanting of a pacemaker. However, it should be understood that the connector is typically rotated 90.degree. counterclockwise and the housing 24 is rotated 180.degree.. With respect to FIG. 2, the redundant electrical lead wire 27 is wrapped by hand around the heart pacemaker 10 by the surgeon to create one or more coils 29. The pacemaker 10 is then introduced into the pocket. As a consequence of the physical size of patients varying substantially and pacemakers coming with only standard lengths of the electrical lead 16, the surgeon is faced with the task of coiling one or more coils 29 around the periphery of the pacemaker 10 in a direction perpendicular to the thickness of the unit. These coils 29 must be held in place by the surgeon's fingers and introduced into the pocket formed underneath the incision 14. This procedure requires delicate manipulations of the surgeon's fingers.
The prior art, as illustrated in FIGS. 1 and 2, has a number of disadvantages. In the first place, when redundant electrical lead 27 is present, buckling of the lead may occur which also can cause undue loading in a portion of the lead 16 which could cause breakage or couple force to the right ventricle as described above. Additionally, the redundant lead 27 may interfere with sensing by the generator. Furthermore, the wrapping of the lead around the periphery of the housing 24 is a cumbersome and potentially time consuming process. The insertion of the lead wrapped around the periphery of the housing 24, as illustrated in FIG. 2, can be difficult. If the one or more coils 29 fall away from the periphery of the housing during placement within the pocket, it is necessary for the surgeon to rewrap the coils. As a result, additional time can be required in completing the surgical procedure of implanting the pacemaker with the attendant increase in costs consequent from payment of operating room and hospitalization fees. Redundant lead wire 27 positioned under the generator against the chest wall can decrease sensing sensitivity by electrical interference. Redundant lead wire 27 positioned above the generator and below the skin can interfere with the conventional generator programming which is performed in and out of the operating room by causing undesirable electrical interference. Finally, since the implanting of a pacemaker is not done under general anesthesia, prolonged operating time required for positioning the coiled redundant wire in place into the subcutaneous pocket can result in additional discomfort to the patient.
The prior art, as illustrated in FIGS. 1 and 2, does not provide any mechanism for retaining redundant lead 27 on the pacemaker in a fixed position to facilitate the elimination of redundant lead. Even if the surgeon is able to coil the electrical lead around the periphery of the generator housing 24 to eliminate the redundant lead 27 of FIG. 1, the likelihood is that the surgical procedure was complicated by requiring delicate and time-consuming manipulations of the redundant wire in coiling it around the periphery of the pacemaker.
German Offenlegungsschrift 27 20 662 discloses a pacemaker system which attaches redundant lead to the body of the pacemaker with a continuous or spaced apart clamps which permit attachment of redundant lead around the periphery of the pacemaker perpendicular to a thickness of the housing of the pacemaker. However, the continuous or spaced apart clamps have the disadvantage of being fixed to the housing of the pacemaker and not easily shifted with respect to the housing during the surgical procedure which prevents the surgeon at the time of positioning the redundant lead in the clamps from easily shifting the position of the clamps with respect to the housing. The inability to easily shift the position of the clamps during surgery makes it more difficult for the surgeon to deftly manipulate the clamps with respect to the housing to eliminate bulges especially at a point at which the electrical lead is attached to the pacemaker or the point where the electrical lead enters the subclavian vein to avoid the potential transmission of force to the ventricular wall. As a result, the disclosed system could be difficult to use in taking up redundant lead during a surgical procedure and the inventor is not aware of this device being commercialized.
U.S. Pat. No. 3,598,124 discloses a lead storage for a pacemaker in which the electrical lead is free to be released as a consequence of the signal generator being free to rotate to play out additional lead as the patient grows which is a common problem for pediatric pacemakers. The pacemaker of the '124 patent does not retain the lead in a fixed position around the periphery of the housing in accordance with the desired procedure as illustrated in FIG. 2. The '124 patent teaches that redundant lead is "an unsatisfactory situation where the extra lead lies within the body". Moreover, the '124 patent teaches that "normal movement of the body may cause problems with the loose extra lead length causing it to, for example, undesirably entwine itself around a portion of the body".
U.S. Pat. No. 4,013,081 discloses a pediatric cardiac pacemaker in which extra electrical lead is coiled and retained within a bag such that, as the patient grows, a large spiral path around the pacemaker can tighten to a smaller spiral to accommodate the greater distance between the heart and the pacemaker as the patient grows. The '081 patent does not retain the lead in a fixed position with respect to the periphery of the pacemaker.
It is estimated that the vast majority of pacemakers which are implanted currently use fixed length leads for patients who are fully grown.